Motor mount for small high speed motors

ABSTRACT

A motor mount for small high-speed motors, consisting of radial and axial bearing components. The axial bearing is configured as a magnetic bearing and the radial bearing as an air bearing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to low-power high-speed motors which are operatedat speeds of up to 20,000 rpm, and more particularly to a bearing thatoperates with the lowest possible friction and without play for suchmotors.

2. Discussion of Related Art

Motors of the type to which the present invention applies are typicallyemployed as the drive in disk storage devices, as well as in the drivesfor scanners, copiers and similar small devices.

All such motor designs have in common the fact that a rotor dome, whichis driven to rotate, is arranged on a stationary base flange and issupported on the base flange with appropriate axial and radial bearings.It is a known drive principle to arrange a stator package on the baseflange so that it works together with a magnet arranged over an air gapwith a driven rotor on the inside, that is, the so-called rotor dome.Thus, rotation of the rotor dome is induced by the magnetic return dueto an appropriately applied rotational field in the stator package.

It is customary with such low-power motors to equip the rotor, that is,the rotor dome, which is rotating at a high rpm, with radial and axialbearings. The bearings should operate with the lowest possible friction.A typical design for such a bearing arrangement consists of using agrooved ball bearing which acts both as a radial bearing and as an axialbearing. Such ball bearings have the disadvantage that they must belubricated and may sometimes cause mechanical vibrations which areunwanted and shorten the useful life of the motor. Furthermore, thisvibration can have a negative effect on the object arranged on the rotordome, for example, a data storage device (hard drive), so that accuracyin reading and writing is thereby impaired.

It is also known that the radial bearing component can be separated fromthe axial bearing component by arranging two different bearings, each ofwhich assumes one bearing function. It is known that a so-called needlebearing or roller bearing, which takes up the radial bearing component,may be used as the radial bearing, and it is also known that a ballbearing or a fluid bearing may be used as the axial bearing.

Additionally, the bearing combination of two air cushion bearings or twofluid bearings is known. In this case it is known that an air cushionbearing is provided to take up the radial bearing components as well asa second air cushion bearing which is provided to take up the axialbearing components.

The arrangement of an air cushion bearing to take up axial bearingcomponents is relatively difficult and expensive because the requiredtolerances in this axial bearing clearance must be kept very narrow,which greatly increases the manufacturing costs of such a bearing.

U.S. Pat. No. 5,289,067 discloses a small motor having radial and axialbearing components. A rotationally driven rotor dome is mounted on ashaft of a stationary base flange by the bearing components. The radialbearing is designed as a hydrodynamic bearing and the axial bearing isdesigned as a passive magnetic bearing in the form of a ring-shapedpermanent magnet in which a magnetically active metal disk is arrangedcentrally and has a rotationally fixed connection to the rotor dome.

SUMMARY OF THE INVENTION

A primary purpose of this invention is to improve upon a low-power motorhaving a bearing arrangement of the type defined above so that in thecase of the presence of a radial bearing of any type, the cost ofproduction of the respective and separate axial bearing is significantlyreduced, while at the same time achieving substantially improved bearingproperties.

An important feature of this invention is that a magnetic axial bearingis designed as an active magnetic bearing and has two coils which serveto produce two independent magnetic fields which act on the metal diskarranged between the two coils, with the metal disk being attached in arotationally fixed but detachable manner to the rotor dome by themagnetic force of a permanent magnet.

An important advantage of the invention is that now a magnetic bearingdesigned as an active magnetic bearing is used as the axial bearing.

In a first embodiment of the present invention, the active magneticbearing operates on one side against a magnetic bias, while in a secondembodiment, the active magnetic bearing operates on two sides against amagnetic bias applied from both sides.

Another significant feature of this invention is that the axial magneticbearing is arranged on one side, that is, on the one side of the rotordome, and not on both sides. This yields the important advantage thatthe bearing is much less expensive because, thanks to this arrangement,the axial magnetic bearing is capable of accommodating both axial forcesacting in one direction is well as in the other direction, althoughthere is only a single bearing. This also yields the additionaladvantage that dismantling is simplified because the rotor dome can beremoved simply by lifting it up, so the axial magnetic bearing arrangedinside the rotor dome is separated. Thus, it is not necessary todismantle a second bearing (not included in this configuration) as mightbe the case in the known related art.

It is thus important that the active magnetic bearing can be arrangedeither on the top inside of the rotor dome or in a different embodimenton the lower side of the rotor dome. In both embodiments, it isimportant that only a single axial magnetic bearing is present, becauseit operates against biases on both sides so that it is capable of takingup the axial bearing forces acting in both directions. This greatlyreduces the cost of manufacturing such a low-power motor, andfurthermore, the rotor dome is stabilized because it is protectedagainst tilting by the axial magnetic bearing. There are no mechanicalvibrations such as those known to occur with mechanical bearings, andthus it runs more smoothly and quietly. This also results in an improveduseful life for the motor.

In a preferred embodiment of the present invention, the axial magneticbearing consists essentially of a coil with a magnetic return ring whichis thermally separated from the radial air cushion bearing. This coilacts in the axial direction on an armature which is consequentlyattracted by this coil to varying extents in the axial direction. Afterthe armature is fixedly connected to the rotor dome, the rotor dome isthus more or less adjusted in the axial direction due to appropriateenergization of the coil in the axial direction.

The axial bias of the rotor dome against which the coil, which receivesan electric current, operates is achieved in the first embodiment bymeans of two oppositely polarized permanent magnets which, for example,repel one another with their two identical poles and thus exert arepulsion effect on the rotor dome which is in turn counteracted by thecoil receiving the electric current. In this way, the axial bearing playof the rotor dome can be adjusted with an extremely high precisionthrough the electric current acting on the coil.

To set a certain dimension, it is preferable to use a sensor thatmonitors the axial bearing play and is connected to the power supply ofthe coil through an assigned control system, thus guaranteeing automaticcontrol of the bearing play at a constant level. This bearing play is,of course, designed to be adjustable.

Various embodiments of position sensors may be used here. In a firstembodiment, there is a sensor that acts by capacitance or inductance,measuring the distance in the bearing gap from a stationary face to theopposite rotating face and detecting it accordingly. In anotherembodiment, the sensor may be designed as an optical sensor, and theadjustment of the axial bearing play may take place by means of anoptical sensor.

In a third embodiment, an inductive sensor may be provided in such amanner that a stationary induction coil in which a suitable inductionvoltage is induced is arranged opposite the rotating magnet arranged inthe rotor dome. Depending on the size of the axial air gap between thesetwo parts, an induction voltage of various levels is induced in theinduction coil in direct proportion to the axial bearing play. Likewise,the bearing play can also be regulated with a high precision in thisway.

In another embodiment of the present invention, instead of a permanentmagnetic bias of the rotor:dome in the axial direction, an active biascan be produced by two oppositely directed coils forming an air gapbetween them by the rotation of a disk in fixed rotational connection tothe rotor dome. Depending on the current acting on the upper and lowercoils, the metal disk which is fixedly connected to the rotor dome ismoved upward or downward axially, thus also adjusting the magneticbearing accordingly.

Whereas in the first embodiment a current-carrying coil and a pairedarrangement of permanent magnets was used, in the second embodiment twocurrent-carrying coils are used, forming an. air gap between them wherea metallic and magnetically active disk rotates, the disk being attachedto the rotor dome in a rotationally fixed manner. Depending on thecurrent flowing in the upper and lower coils, the disk connected to therotor thus moves upward or downward axially, again with precise controlof this axial adjustment play being achieved due to the above-mentionedposition sensor and the above-mentioned control.

In a third embodiment of the present invention, an air cushion bearingis again combined with an axial magnetic bearing, but in this case theair cushion bearing does not function as a purely radial bearing butinstead is capable of taking up both radial and axial bearingcomponents. It is preferable here if this air cushion bearing isdesigned as a toroidal bearing which, by definition, takes up both axialand radial bearing components.

In the design of the active magnetic bearing as an axial bearing, thetwo above-mentioned embodiments are again possible. This means that itis preferable according to this invention if a cylindrical air cushionbearing or a toroidal bearing is used as the radial bearing, while amagnetic bearing is always used as the axial bearing.

In another embodiment, the bearing pair combining the above-mentionedradial and essentially cylindrical air cushion bearing with an axial aircushion bearing which is in turn combined with the above-mentioned axialmagnetic bearing is also used. This design uses an air cushion bearingarrangement consisting of a radial air cushion bearing in combinationwith an axial magnetic bearing. This also yields some importantadvantages because more accurate axial positioning of the rotor dome ispossible due to a well-thought-out arrangement of an additional axialair cushion bearing. This additional axial air cushion bearing then actsas an additional carrier which stabilizes the tilting vibrations andthus also leads to a further improvement in the smooth running of therotor.

BRIEF DESCRIPTION OF THE DRAWING

The objects, advantages and features of the invention will be morereadily appreciated from the following detailed description, when readin conjunction with the accompanying drawing, in which;

FIG. 1 is a partial sectional view of a first embodiment of a bearingaccording to the invention, showing a radial air cushion bearing, anaxial magnetic bearing, and a permanent magnetic bias;

FIG. 2 is partial sectional view through a second embodiment of theinvention having a radial air cushion bearing and a double-acting axialmagnetic bearing;

FIG. 3 is an enlarged detail of FIG. 2; and

FIG. 4 shows another embodiment, in section, of this invention, having atoroidal air cushion bearing in combination with an axial magneticbearing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to the drawing, and more particularly to FIG. 1, baseflange 1 is formed with central recess 2 in which shaft 3 is fixedlymounted by screw 4. The base flange has in its recess 5 stator package 6consisting essentially of inner sleeve 10 from which the core with thestator winding extends radially outward in a known way.

Rotor dome 9 is rotationally mounted on shaft 3 and has on its lowerinside a ring magnet 7 which is arranged on the periphery of the rotordome and is entrained by the rotational field generated in statorpackage 6. The ring magnet is inserted radially outward into magneticreturn ring 8 which closes the magnetic circuit in the rotor. Bearingsleeve 11 is arranged on shaft 3 in a rotationally fixed manner, itsradial outside being designed as air cushion bearing 12.

The FIG. 1 embodiment illustrates that the air cushion bearing isdesigned as a radial bearing and extends over a suitable axial length ofbearing sleeve 11. Furthermore, there are air channels 14 emanating fromconnection channel 15, these air channels in turn leading to connectionchannels 13 which supply the entire air cushion bearing 12 with air fedin from the outside.

It is important here that air cushion bearing 12 has a spiral groovestructure, which is not shown in detail here, and with which it ispossible for air to be automatically drawn in through connecting channel13 while rotor dome 9 is rotating, and to be fed under pressure into aircushion bearing 12. This yields a self-supplying air cushion bearing 12which has an appropriate rigidity at higher rotational speeds.

Bearing sleeve 11 has thermal insulation 16 on the inside which is alsodesigned as a sleeve and is made of a material with low thermalconductivity. Radially on the inside of the thermal insulation 16 thereis outer magnetic return ring 17 on which coil 18 is in turn arranged onthe inside. Radially inward from coil 18 is inner magnetic return ring19. The two magnetic return rings 17 and 19 are magnetically connectedto one another. When a DC electric current is applied to coil 18, thecoil acts in the axial direction on gap 54 at the upper end.

At a slight distance from the upper end side of coil 18 is arrangedarmature 20, which is connected to rotor dome 9 in a rotationally fixedmanner and is in turn sealed by cover 21, which is made of metal.Armature 20 is thus pulled in the axial direction by the end face ofcoil 18 to varying extents, depending on the extent to which the coil issupplied with a DC current.

In contrast with the attractive effect of coil 18 on armature 20, amagnetic bias is provided which in the embodiment shown here consists oftwo similarly polarized permanent magnets 22, 23, with permanent magnet22. being arranged in cover 21 in a rotationally fixed manner andconsequently rotating with rotor dome 9, while permanent magnet 23 isconnected to inner magnetic return ring 19 in a fixed manner. Betweenpermanent magnets 22, 23, a repulsive force is thus generated in thearea of distance 24, counteracting the attractive force of coil 18 onarmature 20. Thus, gap 54 between the end face of magnetic return rings19, 17 and the bottom side of armature 20 can be adjusted with a veryhigh precision. Furthermore, to regulate this distance, position sensor29 is arranged in stationary permanent magnet 23 to detect distance 24from the opposite rotating face and to control the coil currentaccordingly. The bearing gap is also continued in the form of air gap25.

As was mentioned previously, in the case of modifications of thisinvention air cushion bearing 26 may be provided instead of bearing gap25, so that radial air cushion bearing 12 shown here can still becombined with air cushion bearing 26 which acts in the axial direction.Moreover, rotor dome 9 also has air gaps 27, 28 in addition to thestationary parts of base flange 1 to guarantee free rotation.

FIGS. 2 and 3 illustrate an additional embodiment where, instead ofcreating a permanent magnetic bias on rotor dome 9, a controllablemagnetic bias can be generated by the fact that two oppositely polarizedcoils 34, 35 create an air gap 40 between them in which a magneticallyactive metal disk 36 rotates.

It is proposed here that lower stationary coil 35 be arranged on theshaft in coil return 42, opposite upper coil 34 which is also stationaryin coil return 41. The above-mentioned air gap 40, in which themagnetically active metal disk 36 rotates, is arranged between the twocoils 34, 35. It is important here that metal disk 36 is connected tothe rotor dome in a rotationally fixed manner. A special arrangement isprovided for connecting metal disk 36 to the rotor dome.

As explained previously, the rotor dome is connected to cover 21. Arecess is provided on the inside of the cover, with magnet 37 beingmounted in this recess by means of fastening device 38. Thus, magnet 37rotates together with the cover and the rotor dome.

The inside perimeter of disk 36 is in contact with cover 21 on centeringbevel 39, so that metal disk 36 is centered precisely with respect tocenter line 45. Magnet 37 attracts this metal disk magnetically andentrains it. Thus, the metal disk is centered both axially and radiallyprecisely with respect to center line 45 because of this magneticentrainment.

Thus, simple assembly of the entire arrangement is possible, because todismantle the arrangement, one need only lift up cover 21 together withrotor dome 9, which also lifts magnet 37, thus canceling the magneticattraction for metal disk 36. The metal disk may thus remain in thearrangement and need not be dismantled itself.

A magnetic bearing is now proposed because coils 34, 35 are eachsupplied separately with electric current and generate independentmagnetic fields in air gap 40 between them, causing metal disk 36 tomove more or less upward or downward axially. It is preferable here thatcoils 34, 35 are supplied with electric current so that the metal diskis automatically held in an approximately central area in air gap 40 (onelimination of the control).

In addition, a control is also superimposed on this to guarantee aprecision adjustment of metal disk 36 in air gap 40. To do so,stationary position sensor 43 is again provided, detecting with its endedge an opposite edge 46 on the rotating rotor dome across distance 44.This distance 44 is thus detected continuously by position sensor 43 anda control segment is entered as an actual value. On the basis of FIGS. 2and 3 it can be shown that radial air cushion bearing 12 extends fromposition 31 to position 32.

In order for any disk-shaped data carrier which might also be present tobe entrained with the rotor dome, an entraining element in the form ofspring 33 is provided, which is supported on cover 21 on one side and onthe other side is supported on the top of the disk-shaped data carrier.

In a last embodiment, the above-mentioned magnetic bearing (according toFIGS. 1-3) can be combined with a toroidal air cushion bearing. Such anair cushion bearing 47 is illustrated in FIG. 4 where it can be seenthat this air cushion bearing can take up both axial bearing componentsand radial bearing components and can also be combined with anadditional magnetic axial bearing. Specifically it can be seen here thatthere is a stator 48 in which at least one coil 51 is present, acting onopposite pole 50 which, in turn, has its end face opposite permanentmagnet 49 so that again a carrying force is produced by the fact that anattractive force acting in the direction of arrow 53 is generated in theair gap, while a repulsive force in the direction of arrow 52 isgenerated by the above-mentioned toroidal air cushion bearing. Hereagain, the distance in air gap 40 can be regulated with a high precisionthrough appropriate control.

It can be derived from the embodiment mentioned last that the presentinvention is not limited to a combination of a radial air cushionbearing with an axial magnetic bearing, but it includes a combination ofa radial air cushion bearing and an axial air cushion bearing which, inturn, may also be combined with an axial magnetic bearing. Experimentshave shown that superior smooth running is achieved together with lowmanufacturing cost and a long life at the same time. The termhydrodynamic bearing is understood to refer to an air cushion bearing ora fluid bearing. Instead of air as the bearing medium, a liquid is usedwith a fluid bearing.

What is claimed is:
 1. A motor bearing for a high-speed low power motorcomprising a rotationally driven rotor dome mounted on a shaft mountedon a stationary base flange, said bearing comprising: a hydrodynamicbearing; and an active magnetic axial bearing comprising: a magneticallyactive metal disk; a permanent magnet; a first coil generating a firstmagnetic field; a second coil generating a second magnetic fieldindependent of the first magnetic field; said metal disk beingpositioned between said first and second coils; said first and secondindependent magnetic fields acting on said metal disk, said metal diskbeing rotationally coupled to said rotor dome by the magnetic force ofthe permanent magnet and at least one of the independent magnetic fieldsin a detachable manner.
 2. The motor bearing according to claim 1, andfurther comprising: a rotor dome cover formed with a centering bevel;said metal disk having a central bore therethrough; said metal diskbeing centered radially and axially on its central bore through saidcentering bevel on said cover.
 3. The motor bearing according to claim 1or 2, wherein said metal disk remains between said first and secondcoils even after being released from said rotor dome.
 4. The motorbearing according to claim 1 or 2, and further comprising: a sensor; anymagnetic adjustment in said axial bearing is controlled by means of thecurrent in said first and second coils pursuant to signals from saidsensor.
 5. The motor bearing according to claim 1 or 2, wherein saidaxial bearing operates on two sides against a magnetic bias from bothsides.
 6. The motor bearing according to claim 1 or 2, wherein saidaxial bearing alone as the single magnetic bearing arranged on saidmotor axle takes up the axial forces from both directions.
 7. The motorbearing according to claim 1 or 2, wherein said axial magnetic bearingtakes up radial forces to prevent tilting.
 8. The motor bearingaccording to claim 6, wherein said axial magnetic bearing also takes upradial forces to prevent tilting.
 9. The motor bearing according toclaim 1 or 2, wherein said hydrodynamic bearing is a radial bearingdesigned as an air cushion bearing in the form of a toroidal bearingwhich is suitable for taking up axial forces in addition to radialforces.
 10. The motor bearing according to claim 1 or 2, wherein saidhydrodynamic bearing is a radial bearing comprising an air cushionbearing and a toroidal bearing.
 11. The motor bearing according to claim1 or 2, wherein said axial magnetic bearing is thermally isolated withrespect to said radial bearing.
 12. The motor bearing according to claim10, wherein said axial magnetic bearing is thermally isolated withrespect to said radial bearing.